California reports sixth human case of H5N1 bird flu

Health officials in California have reported another human case of H5N1 avian flu, bringing the total number of dairy farmers infected in the past week to six. All cases were caused by animal-to-human transmission.

According to the California Department of Public Health (CDPH), all six cases so far have been identified in people working on dairy farms in the Central Valley, indicating that none of them were caused by person-to-person transmission.

Of the six cases, four have been confirmed by the Centers for Disease Control and Prevention (CDC). The other two tested positive in California and are awaiting final confirmation from the CDC.

“All cases to date have experienced mild symptoms, including eye redness or discharge (conjunctivitis),” CDPH said in a statement Thursday. “None of the individuals were hospitalized.”

The statement continued: “While the risk to the general public remains low, additional human cases of avian influenza are expected to be identified and confirmed in California in individuals who have contact with infected dairy cows.” CDPH continues to work closely “Work with local health authorities to identify, track, test, confirm and treat possible and confirmed cases of avian influenza in humans.”

Based on the CDC’s genomic sequencing of the first two human avian flu cases in California, there is no evidence of an increased ability of the virus to infect or spread between humans, and there is no known reduced susceptibility to antiviral drugs.

According to CDPH, pasteurized milk and dairy products remain safe to consume because pasteurization is completely effective in inactivating the avian influenza virus. As an additional precaution and in accordance with long-standing state and federal requirements, milk from sick cows is not permitted in the public milk supply.

LINK: A list of all human cases of H5N1 bird flu since 2021

A newer H5N1 strain, clade 2.3.4.4b, has raised concerns due to its global distribution and the growing number of cases in mammals, including outbreaks in dairy cows in the United States. To date, only a limited number of human cases have been reported following contact with infected birds or cows.

Earlier Thursday, officials confirmed that H5N1 bird flu has been detected so far in 99 dairies across California, the country’s largest milk producer. That’s up from 44 earlier this month.

So far this year, 33 human cases of H5N1 avian influenza have been reported, including 20 in the United States, 10 in Cambodia and one each in Australia, Vietnam and China. Only the U.S. cases — 10 in Colorado, 6 in California, 2 in Michigan and one each in Texas and Missouri — were caused by the newer variant, clade 2.3.4.4b.

Last month, a patient in Missouri tested positive for H5N1 bird flu, although there are no known links to infected animals. The patient was hospitalized but has since recovered. The source of infection is still unknown, but no further cases have been reported.